Device for winding a timepiece movement

ABSTRACT

A component of a winding device, in particular an automatic winding device, of a timepiece movement, wherein it is made of austenitic stainless steel and wherein it comprises at least one friction surface hardened by carbon or nitrogen type atoms introduced into the austenitic stainless steel over a predetermined depth.

This application claims priority of European patent application No.EP16184191.1 filed Aug. 15, 2016, the contents of which are herebyincorporated herein in their entirety.

The invention relates to a component of a winding device, in particularan automatic winding device, of a timepiece movement and also to awinding device, in particular an automatic winding device, to atimepiece movement and to a timepiece as such, comprising such acomponent. It also relates to a process for manufacturing a component ofa winding device, more generally of a timepiece movement.

An automatic winding device of the prior art makes it possible, via akinematic chain, to connect an oscillating weight to a barrel, so as toenable the winding-up of a barrel spring.

FIG. 1 illustrates more particularly a portion of a mobile element of akinematic chain of an automatic winding device of the prior art. Thismobile element comprises in particular two clicks 1, 2 that cooperatewith a toothed wheel 3 that is attached to a pinion 4. In a firstautomatic winding mode, corresponding to a first direction of rotationof the oscillating mass, the toothed wheel 3 and the pinion 4 arerotated under the action of the clicks 1, 2 which are both pivoted on anautomaton wheel, not represented in FIG. 1, itself rotated in a firstdirection of rotation. In a second automatic winding mode, correspondingto a second direction of rotation of the oscillating mass, the clicks 1and 2 have no effect on the toothed wheel 3 and the pinion 4, andoscillate at high speed relative to the toothed wheel 3, about theirrespective pivoting axis, under the rotation of the automaton wheel in asecond direction of rotation. In a third manual winding mode, the pinion4 and the toothed wheel 3 are rotated under the effect of a manualwinding chain. The rotation of the wheel 3 disengages the teeth of thewheel 3 from the clicks 1 and 2 which oscillate at high speed, or evenat very high speed, about their respective pivoting axis.

These three winding modes, well known from the automaton devices of theapplicant, are especially rendered possible by the asymmetricconformation of the teeth of the wheel 3, and also by the specificgeometry of the clicks 1, 2, in particular of the beaks of the clicks 1,2. In the three modes, the beaks of the clicks 1, 2 cooperate with theteeth of the toothed wheel 3 and there is a friction torque between thefriction surfaces of these components, which generates wear phenomenawith aging. The second and third winding modes stress the componentsmore greatly on the tribological level due to the oscillations at highspeed, or even at very high speed, of the clicks: specifically, frictionrates are measured in the case of a click of at least 5 kHz in manualwinding, which may even exceed 10 kHz. By way of indication, theoscillation frequencies of the axes of a mechanical oscillator of atimepiece movement are in general of the order of 3 to 5 Hz, whichrepresents very different stresses than those of a winding device. Theclicks and the toothed wheel are in general stamped from steels of Ck60,Finemac or 20AP type. With these embodiments from the prior art,pronounced wear appears during advanced aging of the automaton device,as is described in detail below. This wear degrades the efficiency ofthe automaton and this leads to a risk of loss of winding performanceafter advanced aging.

FIGS. 3a and 3b specifically represent the friction surfaces of a clickfrom the prior art made of Ck60 steel after aging, respectively as achemical contrast scanning electron microscopy (SEM) image and as anoptical microscopy image. It appears that a large portion of the surfaceof the functional zone, identifiable by darker zones in these figures,has changed with the aging. FIG. 4 illustrates the results of thechemical analysis of these surfaces by EDX microprobe: the dark zonescorrespond to the presence of oxidation products, which turn out to beiron oxide.

The pronounced formation of oxide on the friction surfaces is typical ofthe tribo-oxidation mechanism. Furthermore, the optical images show morespecifically that the oxide on the surfaces has a brown to red color,typical of hematite (Fe₂O₃), which is a mineral, the hardness of whichis substantially 1000-1100 HV, which originates from waste of mixturesof oxides that form on the two surfaces in contact before becomingencrusted on each surface. The initial Ck60 steel has a hardness of theorder of 720 HV. The mineral deposited with aging consequently has ahigh abrasion potential relative to the softer metal surfaces. The wastegenerated by the tribo-oxidation is therefore one of the causes of thedegradation of the performances observed during the aging of the windingdevice from the prior art. The applicant has therefore identified, forthe first time, the presence of a corrosion phenomenon that appears atthe interface between the two components of the winding device and morespecifically the appearance of an iron oxide, which causes acceleratedwear.

Moreover, the overall aging of a winding system is also linked to thewear of components other than those of a winding device as described indetail above: the solution of the prior art is based on a winding devicethat therefore accentuates the overall wear of a winding system.

The objective of the present invention is to propose an improvedsolution for a winding device, in particular an automatic windingdevice, of a timepiece movement, which does not comprise all or some ofthe drawbacks of the prior art.

Thus, a general objective of the invention is to propose a timepiecemovement winding device that has improved behavior with respect toadvanced aging relative to the solutions of the prior art. For this, theinvention seeks to achieve one of the following two subjects:

-   -   a first subject consists of a timepiece movement winding device        which has a substantially constant performance over time; or,        more ambitiously,    -   a second subject consists of a timepiece movement winding device        which has a performance that increases with time in order to        reduce, as much as possible, the overall aging of a winding        system.

More specifically, the invention therefore seeks a solution ofcomponents for a timepiece movement winding device that withstandscorrosion better, even at very high friction frequencies, in particulargreater than or equal to 5 kHz.

For this purpose, the invention is based on a component of a windingdevice, in particular an automatic winding device, of a timepiecemovement, wherein it is made of austenitic stainless steel and whereinit comprises at least one friction surface hardened by reinforcing atomsintroduced into the austenitic stainless steel over a predetermineddepth.

More specifically, the invention is based on a winding device, inparticular an automatic winding device, of a timepiece movement,comprising two metal components that cooperate through an interface thatis subjected to friction, wherein it comprises at least one austeniticstainless steel component, comprising at least one friction surfacehardened by carbon or nitrogen type atoms introduced into the austeniticstainless steel over a predetermined depth.

The invention is more specifically defined by the claims.

These subjects, features and advantages of the present invention will bedisclosed in detail in the following description of one particularembodiment given non-limitingly in connection with the appended figures,among which:

FIG. 1 represents a portion of a mobile element of a kinematic chain ofa winding device of the prior art.

FIG. 2 represents a click of a mobile element of a kinematic chain of awinding device according to one embodiment of the invention.

FIGS. 3a and 3b represent the friction surfaces of a click from theprior art made of Ck60 steel after aging.

FIG. 4 illustrates the results of the chemical analysis of the frictionsurfaces from FIGS. 3a and 3b of the click from the prior art by EDXmicroprobe.

FIGS. 5a and 5b represent the friction surfaces of a click after agingaccording to one embodiment of the invention.

FIG. 6 illustrates the results of the chemical analysis of thesefriction surfaces from FIGS. 5a and 5b of the click according to theembodiment of the invention by EDX microprobe.

FIG. 7 represents the results of comparative tests of clicks from theprior art and from the embodiment of the invention.

According to the embodiment that will be described, the inventionrelates to a click and a toothed wheel of an automaton device orautomatic winding device of a timepiece movement. According to thisembodiment, the click is designed to cooperate with the teeth of thetoothed wheel. More particularly, the click is pivoted so as tocooperate with the teeth of the toothed wheel by means of beaks inparticular positioned at its ends. Alternatively, the click could bedesigned to cooperate with teeth and/or a cam of the automatic windingdevice, with or without return spring. More generally, this inventioncould be implemented on any other component of a winding device that issubjected to friction, in particular on any pair of metal componentscomprising an interface that generates high-frequency friction. It couldfor example be implemented on a ratchet click of a winding device,whether it is a manual or automatic winding device.

FIG. 2 illustrates a click 12 of a winding device according to oneembodiment of the invention. This click comprises two beaks 13, 14 atits two ends, which cooperate alternately with a toothed wheel, such asthe toothed wheel 3 of FIG. 1, according to the three modes of operationused for the winding, as explained above. On each of these beaks 13, 14,a friction surface 15, 16 of a functional zone which is subjected to thefriction torque with the toothed wheel has respectively been identified.

In order to overcome these phenomena, the embodiment proposes tomanufacture the click 12 from an austenitic stainless steel, for examplea steel of 316L type, the friction surfaces 15, 16 of which aresubjected to a particular treatment that consists in diffusing carbon ornitrogen atoms over a given depth. This click is designed to cooperatewith a conventional toothed wheel, for example made of 20AP or Finemactype steel.

The process for manufacturing such a click according to the embodimentcomprises the following steps:

-   -   stamping the click from a 316L austenitic stainless steel strip;    -   treating at least one friction surface of the click, consisting        in diffusing reinforcing atoms of carbon or nitrogen type into        the crystal lattice of the steel over a predetermined depth,        preferably between 5 and 40 microns inclusive. This treatment        may consist in subjecting the timepiece to a gas (methane or        propane for carburization, ammonia or molecular nitrogen for        nitridation and a mixture of the two for nitrocarburization), at        a temperature below 500° C., in order to prevent the formation        of chromium carbides or chromium nitrides. By way of example,        this treatment may consist of a Kolsterisation® or a        thermochemical treatment such as a case hardening, a        nitridation, a nitrocarburization, an ion implantation, a        diffusion heat treatment, etc. This treatment is selected so as        to obtain a hardening of the treated surfaces to a hardness        greater than or equal to 1000 HV. Such a treatment is not        described in detail since it is a question of using a technique        known from the prior art.

Advantageously, the process comprises a polishing step between thepreceding two steps. It also advantageously comprises a final polishingstep after the treatment step, the role of which is to flatten thefriction surfaces, for example over 2-3 μm, in order to make the treatedsurfaces perfectly smooth.

FIGS. 5a and 5b illustrate the friction surfaces observed after the sameaging protocol of the click according to the embodiment as that of theprior art illustrated in FIGS. 3a and 3b . It is clearly apparent thatthe friction surfaces of the click according to the embodiment of theinvention now have hardly any dark zones, unlike the observationdescribed with reference to FIGS. 3a and 3b . Furthermore, the chemicalanalysis, the results of which are illustrated by FIG. 6, shows that thefew dark marks are due to oxide of iron and/or of chromium, inparticular chromite (FeCr₂O₄), which is responsible for the superioroxidation resistance of the click according to the embodiment duringfriction. As an observation, the iron oxide observed on the click ismainly formed on the toothed wheel then transferred to the surface ofthe click.

FIG. 7 also illustrates the effect obtained with the winding deviceaccording to the embodiment. This figure represents the torques measuredon a winding device of the prior art, between a Ck60 steel clickcombined with a 20AP steel toothed wheel, by the bars, 21, 31, 41, 51,61, 71 in a new state respectively for several speeds at the ratchet andby the bars 23, 33, 43, 53, 63, 73 in an aged state respectively for thevarious speeds at the ratchet, compared to the torques measured on thewinding device according to the embodiment of the invention, by the bars22, 32, 42, 52, 62, 72 in a new state respectively for the variousspeeds at the ratchet and by the bars 24, 34, 44, 54, 64, 74 in an agedstate respectively for the various speeds at the ratchet. The aging wasobtained by manually winding the watch by the stem, which corresponds tothe third mode of operation of the device, thus giving rise to therotation of the toothed wheel and its friction against the click whichoscillates according to its pivot axis. As an observation, it is aquestion here of the harshest wear conditions for the clicks since theyare always in unclicked configuration and oscillate, in particular rub,at high speed against the toothed wheel.

FIG. 7 shows that before aging, the torque measured for the componentsaccording to the embodiment of the invention is very slightly lower thanthat measured for the components of the prior art. After aging, the gapbetween the two measurements becomes very significant. The componentsaccording to the embodiment of the invention have a torque reductionwhereas the components of the prior art have a radical increase in thetorque measured, which illustrates their significant reduction inperformance over time.

Thus, against all expectations, the solution used by the embodiment ofthe invention even makes it possible to reduce the friction torques overtime, which enables the winding device to improve its performance whileaging. This effect is very advantageous since it makes it possible, forexample, to compensate for the aging of the winding system linked to thewear of other components. Another advantage of the invention originatesfrom the fact that the timepiece movement winding device is lesssensitive to magnetism due to the materials used.

The embodiment has been described using a click made of treatedaustenitic stainless steel, combined with a standard wheel. As avariant, the wheel may likewise be made of austenitic stainless steel,and its teeth, at least their friction surfaces, may be hardened by atreatment as described above.

Moreover, the austenitic stainless steel selected in the embodiment isof 316L type, but any other austenitic stainless steel could be used,such as 304L or 904L.

Naturally, the invention is not limited to the winding device describedand could as a variant be implemented on any other metal component of awinding device that has any other structure, more specifically on atleast one of its components that is subjected to frictional wear.

The invention also relates to a timepiece movement that comprises awinding device, in particular an automatic winding device, as describedabove. It also relates to a timepiece, such as a wristwatch, whichcomprises such a timepiece movement.

Moreover, the invention may more generally be extended to any metalcomponent of a timepiece movement subjected to significant frictionagainst another metal component, for example a lever, in particular alever beak which is designed to cooperate with a cam, in particularwithin the context of a retrograde mechanism. It may also be implementedon the links of a steel strap, which are also subjected to a lot offriction through contact with their axes of rotation.

The invention claimed is:
 1. A winding device of a timepiece movement, comprising: first and second metal components that cooperate through an interface that is subjected to friction, wherein at least the first of the metal components is an austenitic stainless steel component, wherein the first of the metal components comprises at least one first metal friction surface, wherein the second of the metal components comprises at least one second metal friction surface, the at least one first metal friction surface being configured to be subjected to friction against the at least one second metal friction surface at the interface, wherein the at least one first metal friction surface is hardened by carbon or nitrogen type atoms introduced into the austenitic stainless steel over a predetermined depth, and wherein the first and second metal friction surfaces of the first and second metal components are configured to be subjected to friction at the interface at a rate of at least 5 kHz.
 2. The winding device as claimed in claim 1, wherein the predetermined depth is between 5 and 40 μm inclusive.
 3. The winding device as claimed in claim 2, wherein the at least one hardened fiction surface has a hardness greater than or equal to 1000 HV.
 4. The winding device as claimed in claim 3, wherein the austenitic stainless steel is of 316L, 304L or 904L type.
 5. The winding device as claimed in claim 3, wherein one of the first and second components is a click and the other of the first and second components is a toothed wheel cooperating with the click.
 6. The winding device as claimed in claim 2, wherein the austenitic stainless steel is of 316L, 304L or 904L type.
 7. The winding device as claimed in claim 2, wherein one of the first and second components is a click and the other of the first and second components is a toothed wheel cooperating with the click.
 8. The winding device as claimed in claim 1, wherein the at least one hardened fiction surface has a hardness greater than or equal to 1000 HV.
 9. The winding device as claimed in claim 8, wherein the austenitic stainless steel is of 316L, 304L or 904L type.
 10. The winding device as claimed in claim 8, wherein one of the first and second components is a click and the other of the first and second components is a toothed wheel cooperating with the click.
 11. The winding device as claimed in claim 1, wherein the austenitic stainless steel is of 316L, 304L or 904L type.
 12. The winding device as claimed in claim 11, wherein one of the first and second components is a click and the other of the first and second components is a toothed wheel cooperating with the click.
 13. The winding device as claimed in claim 1, wherein one of the first and second metal components is a click and the other of the first and second metal components is a toothed wheel cooperating with the click.
 14. A timepiece movement comprising a winding device as claimed in claim
 1. 15. A timepiece comprising a timepiece movement as claimed in claim
 14. 16. A process for manufacturing a timepiece movement winding device, wherein the process comprises: manufacturing at least one metal component, wherein the manufacturing comprises: forming the component into an austenitic stainless steel strip; and treating at least one friction surface of the component obtained, wherein the treating comprises integrating reinforcing atoms of carbon or nitrogen type over a predetermined depth, so as to obtain the timepiece movement winding device as claimed in claim
 1. 17. The process for manufacturing a winding device as claimed in claim 16, wherein the treating comprises subjecting the timepiece to a gas at a temperature below 500° C., in order to prevent the formation of chromium carbides or chromium nitrides, or to a thermochemical treatment.
 18. The process for manufacturing a winding device as claimed in claim 17, comprising polishing, wherein the polishing is performed at least one of (i) between the forming and treating and (ii) on at least one treated friction surface after treating.
 19. The process for manufacturing a winding device as claimed in claim 16, comprising polishing, wherein the polishing is performed at least one of (i) between the forming and treating and (ii) on at least one treated friction surface after treating.
 20. The process for manufacturing a winding device as claimed in claim 16, wherein the treating comprises subjecting the timepiece to a gas, wherein the gas is selected from the group consisting of a carburization gas selected from methane and propane for a carburization, a nitrididation gas selected from ammonia and molecular nitrogen for a nitridation, and a mixture of a carburization gas selected from methane and propane and a nitridation gas selected from ammonia and molecular nitrogen for a nitrocarburization.
 21. The process for manufacturing a winding device as claimed in claim 16, wherein the treating comprises subjecting the timepiece to a thermochemical treatment selected from the group consisting of a case hardening, a nitridation, a nitrocarburization, an ion implantation, and a diffusion heat treatment. 